The present invention relates to a method for manufacturing an image display element used in televisions and flat panel displays on which computer images are displayed. More particularly, the present invention relates to a method for manufacturing an image display element using a resin substrate.
Conventionally, in liquid crystal panels (liquid crystal display elements) that use a resin substrate, the resin substrate undergoes significant dimensional change with variations in absorption of moisture into the resin substrate and in ambient temperatures. Thus, dimensions of an etching pattern of ITO (indium tin oxide) electrodes and a CF (color filter) pattern, for example, may be wildly different from an actual dimension. Similar problems occur when an array substrate and an opposing substrate are bonded together. An electrode pattern and a color filter pattern tend not to match with each other between the bonded substrates. Consequently, the size of a pixel (aperture ratio) varies. This affects on display characteristics such as contrast.
As an approach to solve the above-mentioned problems, Japanese Patent Laid-open No. 9-146080 disclose a technique in which a gas barrier film is disposed on a resin substrate to prevent any gases from infiltrating into a liquid crystal and the dimensional change caused by the absorption of moisture is suppressed as a side effect of the gas barrier film. Typical gas barrier films include SiOx films and SiNx films.
However, the resin substrate having the gas barrier film cannot completely avoid the absorption of moisture. It was found that the substrate undergoes no rapid dimensional change when it is left at a room temperature, but undergoes significant dimensional change before and after heating of the substrate. This means that the resin substrate would undergo significant dimensional change even when it has a gas barrier film because a process for manufacturing liquid crystal panels involves repeated heating steps. To solve this problem has been a big challenge.
The present invention was made to solve the above-mentioned problems, and an object thereof is to provide a method for manufacturing an image display element of which resin substrate undergoes less dimensional change.
In order to achieve the object, the present inventor observed dimensional behaviors of resin substrates thoroughly. As a result, it was revealed that change in water absorption into the resin substrate during repeated heating is responsible for the dimensional change due to the repeated heating of the resin substrate.
Therefore, a method for manufacturing an image display device according to the present invention is a method for manufacturing an image display element having a resin substrate that holds a display functional portion on which images are displayed, characterized by comprising: an inorganic film forming step of forming inorganic films on both surfaces of the resin substrate, and a dehydration step of dehydrating the resin substrate before or after the inorganic film forming step, wherein the resin substrate subjected to the inorganic film forming step and the dehydration step and an other substrate are bonded to each other by a sealing material, and then the sealing material is cured by heating at least the resin substrate. With this configuration, the water absorption into the resin substrate is reduced. The resin substrate is covered with the inorganic films on both surfaces thereof, so that the water absorption into the resin substrate is kept at the reduced level after a relatively long period of time. Consequently, variation in water absorption is small when the resin substrate is subjected to heating in subsequent steps of manufacturing the image display element. The dimensional change of the resin substrate is small accordingly.
The display functional portion may be interposed between the resin substrate and the other substrate.
In addition, the other substrate may has a color filter. Furthermore, the color filter may comprise subfilters which are color filters corresponding to red, green and blue.
The color filter may be adapted to selectively pass a light having predetermined wave length included in incident white light therethrough.
The resin substrate may be dehydrated in the dehydration step so that the water absorption is 0.5% or less by weight. With this configuration, the resin substrate having water absorption of 0.5% or less by weight is in chemical absorption of moisture rather than in physical absorption of water. Absorption and removal of water occur less frequently at a relatively high temperature and the dimensional change is much smaller accordingly.
The inorganic film forming step may be carried out after the dehydration step.
The dehydration step may be carried out after the inorganic film forming step.
The resin substrate may be formed of, at least one of epoxy, acryl, polyimide, polycarbonate, polyvinyl alcohol, and polyethylene, composites thereof, or laminated resin materials thereof. This configuration provides good optical properties because of transparency of the resin and provides good reproducibility in water absorption and dimension due to the repeated heating.
The inorganic film may comprise a film of any one of SiOx, SiNx, GeOx, TiOx, and ZrOx, a composite film thereof or a laminated film thereof.
The inorganic film may have a film thickness between 15 nm and 40 nm both inclusive. With this configuration, the water absorption is kept at the reduced level for a long period of time, without any crack produced in the inorganic film.
The resin substrate may be dehydrated by means of heating. With this configuration, the water absorption into the resin substrate can be reduced easily in a highly reproducible manner.
A temperature during the heating may be 200xc2x0 C. or less. With this configuration, it is possible to keep the reproducibility of the water absorption and the dimension (properties of the resin) due to the repeated heating because the resin undergoes less thermal variation.
The resin substrate may be dehydrated by pressure reduction. With this configuration, the water absorption into the resin substrate can be reduced easily in a highly reproducible manner. Moreover, it is possible to keep the reproducibility of the water absorption and the dimension due to the repeated heating because the resin undergoes less thermal variation.
The resin substrate may be heated after the pressure reduction of the resin substrate. With this configuration, the resin substrate is filled with gases in place of impurities such as water. Such gases are less prone to be absorbed and released. The dimensional change of the resin substrate due to the repeated heating is significantly small accordingly.
A temperature during the heating may be 200xc2x0 C. or less. With this configuration, it is possible to keep the reproducibility of the water absorption and the dimension due to the repeated heating because the resin undergoes less thermal variation.
An atmosphere of the heating may be an inert gas. With this configuration, oxidative degradation of the resin can be avoided.
An atmosphere of the heating may be air. With this configuration, the resin substrate is filled with air in place of impurities such as water. Absorption and release of air do not change the composition thereof. Thus, the dimensional change of the resin substrate due to the repeated heating is significantly small accordingly.
A humidity of the atmosphere of the heating may be 35% or less. With this configuration, the dimensional change of the resin substrate due to the repeated heating is significantly small accordingly.
A predetermined film may be formed on one of the inorganic films of the resin substrate and the predetermined film may be patterned after the resin substrate is subjected to the inorganic film forming step and the dehydration step. With this configuration, the predetermined film is formed and patterned on the resin substrate that undergoes less dimensional change due to the repeated heating. Therefore, the dimensional change of the patterns in the predetermined film is significantly small even after the repeated heating in subsequent steps of manufacturing the image display element.
The predetermined film may be a transparent electrode film. With this configuration, the dimensional change of the transparent electrode due to the repeated heating is small.
The predetermined film may be a color filter film. With this configuration, the dimensional change of the color filter due to the repeated heating is small.
The image display element may be a liquid crystal display element, the liquid crystal display element may has the resin substrate as the other substrate, and patterns of the predetermined film may be formed on the resin substrate. With this configuration, the resin substrates that undergo less dimensional change due to the repeated heating are bonded together. Accordingly, less misalignment of the patterns occurs between the bonded resin substrates.
In addition, flexible terminals may be adhered to the transparent electrode formed by means of patterning the transparent electrode film. With this configuration, dimensional change due to the repeated heating of the resin substrate is small. Accordingly, less misalignment of the patterns occurs between the transparent electrode and the flexible terminals.
Furthermore, a method for manufacturing an image display element according to the present invention is a method for manufacturing an image display device having a resin substrate that holds a display functional portion on which images are displayed, the method comprising a reset step of dehydrating the resin substrate so that the water absorption thereof is 0.5% or less by weight. With this configuration, the resin substrate is shrinked to the limit in the reset step. Subsequently, the dimensional change of the resin substrate from the reset step to a predetermined processing step can be estimated based on the resin substrate that is shrinked to the limit, by means of manufacturing the image display element in an atmosphere maintained under predetermined conditions. Thus, the processing can be carried out with high dimensional accuracy by performing the processing such as patterning in prospect of the dimensional change in the predetermined processing step.
An inorganic film forming step of forming inorganic films on both surfaces of the resin substrate may be provided before the reset step. With this configuration, the dimensional change of the resin substrate is small after steps from the reset step to the predetermined processing step. Accuracy of estimating the change would be improved, which allows processing with higher accuracy.
These object as well as other objects, features and advantages of the invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.